In myelodysplasia (MDS) the precise mechanism of ineffective erythropoiesis is not fully elucidated, but it is suggested that apoptosis may contribute to this process. We performed TdT-mediated dUTP-nick end labelling (TUNEL) staining of paraffin embedded bone marrow specimens to assess the amount of apoptotic cells in 21 MDS patients (7 RA, 3 RARS, 5 RAEB, 3 RAEB-T, 3 CMML) and five normal controls. In 10 MDS patients the TUNEL assay was performed in combination with immunostaining for Glycophorin-A (GpA) to determine apoptosis in the maturing erythroid compartment. To assess the proliferation of the bone marrow cells the expression of Ki-67 antigen was used as a marker. The mean apoptotic index (AI) in MDS patients was not increased (2.3 +/- 3.0% in MDS versus 4.8 +/- 1.2% in normal controls (P < 0.05)). Moreover, no significant difference in mean AI was observed in the GpA+ compartment between MDS and normal controls (0.8 +/- 0.2% versus 0.6 +/- 0.1%). In addition the different FAB-classifications and the different International Prognostic Scoring System (IPSS)-risk groups showed no significant differences between the subgroups. The expression of Ki-67, as marker for proliferative activity, in the GpA+ compartment from MDS did not differ significantly from normal controls (84.0 +/- 12.2% versus 79.9 +/- 20.2%). Our findings suggest that the observed increased apoptosis in in vitro culture assays is related to the detachment of the cells from the microenvironment leading to an increased susceptibility to apoptosis.